In rail car truck assemblies of the type to which this invention relates, it is known to provide friction wedges housed within pairs of bolster pockets located on opposite sides of the bolster adjacent its ends. The friction wedges are preferably provided in pairs which are biased upwardly by springs urging them against a sloped surface within a pocket of the rail car bolster and a wear surface which defines a side frame column at an end of the side frame opening.
In a rail car truck of the type that this invention is particularly applicable to, the bolster pockets have a sloped back surface and use a wear insert bearing on the sloped surface. This wear insert is a separate part which interfaces with correspondingly sloped surfaces of a pair of split wedges. It is known to provide the sloped pocket surfaces with a laterally extending taper or bevel so that the biasing force exerted on a wedge causes it to bear against a side wall surface of the bolster pocket. The wedge action within the pocket thus produces biasing forces jointly against the sloped surface of the pocket, the side edge of the side frame opening and against the pocket side walls generating damping forces which keep the truck square, thereby counteracting truck hunting and reducing wheel wear.
U.S. Pat. No. 4,244,298, issued Jan. 13, 1981, and U.S. Pat. No. 5,943,961, issued Aug. 31, 1999, constitute prior art over which the present invention is an improvement. In these patents, wedges are shown which are split into two side-by-side pieces in spaced relationship to one another. According to both of these patents, the two wedges are biased into full-faced engagement with correspondingly sloped sections of the pocket. In both patents, a side of each wedge section is also biased into face-to-face engagement with a side surface of the bolster pocket side wall.
In U.S. Pat. No. 4,244,298, the sloping surfaces of the pocket are integrally formed with the bolster. In practice, this is accomplished either by welding forged inserts into the pocket having the required shape, by casting the pocket with the corresponding shape or by building up the pocket by welding. In the '961 patent, the problems and expense of the required welding operation are eliminated by providing a removable insert having the required shape which is supported within the pocket without any need for welding it in place.
In service, the forces holding the side of a wedge against the side of the pocket, while increasing the capability of the wedges to square the truck, result in wear of the corresponding pocket side wall. Eventually, during the course of normal use of the truck, this wear may be as great as ⅛″ to 3/16″ or even more, requiring a rebuild of the bolster pockets.
Rebuilding a worn pocket is a difficult and time consuming operation at best. One method employed is to build up the pocket with molten material by welding, then grinding to the original pocket dimensions the material added by welding. An alternative method is to weld a small wear pad onto the side wall surfaces of the pocket. However, building up the pocket by either of these methods is a difficult proposition because the interiors of the pockets are relatively inaccessible, being only 5-¾″ to about 7-½″ wide for a typical freight car bolster.